Oil and gas wells are rotary drilled using a drill string and are made up of drill pipe joints. A drill pipe joint is a length of pipe typically about 30 feet long with rotary shouldered tool joints welded to each end, one end being a female threaded tool joint and the other end a male threaded tool joint. A stand of drill pipe typically is three joints of drill pipe. A stand of drill pipe typically has one to five stands of drill collars. A drill collar is a section of heavy wall tube with a rotary shouldered connection located at the bottom of the string adjacent to the drill bit. Drill string connections are commonly called rotary shouldered connections.
Periodically, part or all of the drill string is removed from the hole to change the bit or to add casing as drilling progresses and the bore hole becomes deeper. Casing is permanent lining in the well.
To add or remove drill pipe or drill collar segments to or from the drill string, the existing connections between the segments must be broken loose and rotated counter clockwise multiple times to disengage the threaded connection and separate the segments so that the segment can be removed from the drill string. The pipe sections must be rotated clockwise and retightened to form a tight seal to continue drilling.
The rotating or “spinning” portion of the operation can be done by hand using a chain wrench or with a spinning chain wherein a chain is wrapped around the pipe and pulled by a winch. The hand methods are time consuming and the spinning chain method is dangerous to rig personnel. Accordingly, powered spinning machines are commonly employed; they decrease spinning time and accidents.
Current commercial spinners are pneumatically or hydraulically powered machines which grip the drill pipe with cylindrical rollers, or loops of special chain called silent chain, or special belts. These spinners must grip the drill pipe surface where it is cylindrical and uniform and smooth to preclude damaging the spinner components and to ensure adequate contact between the spinner and the drill pipe to transmit torque.
The transition area, where the tool joint is welded to the drill pipe, is typically rough and irregular from the pipe manufacturing process and is unsuitable to be gripped by conventional spinners. Typically, drill pipe transition zones have their smallest diameter below the drill pipe and the transition zone diameter progressively increases before flaring out quickly on the tool joint to become the tong space. The length of the transition section is typically only a few inches but with conventional spinners the spinner has to be applied well away from the tool joint to ensure that no part of the spinner touches the transition zone. Gripping the transition area using chain type spinners will cause premature failure of the drive chain, typically within hours; the drive chain is an expensive unit. Manufacturers of current spinners specifically instruct operators to keep their spinners away from the transition zone. Accordingly, to keep the spinner away from the tool joint, the spinner must be located a foot or so above the wrench.
Toothed rollers clamped to the tong area of the tool joint have been used. Current operators eschew toothed rollers because they damage the tool joint and sealing surface by trapping shavings between the machined faces of the rotary shouldered connection, damaging the sealing surface.
A drill pipe spinner that can grip the drill pipe on the transition zone would be more compact and cost less than current spinners. It would increase visibility for the roughneck crew and decrease effort to move it thereby reducing crew fatigue. Its compactness would permit the spinner to be used on small drilling rigs which can not accommodate current commercial machines. Transportation of the rig would be easier and safer and present less chance of damaging the machine and be more accessible to remote drilling sites that are difficult to reach with trucks. It would reduce topside weight of offshore rigs. Such a spinner used alone with manual tongs would also be less restrictive and allow the spinner to be placed lower when desired.
A spinner with capability to grip the drill pipe transition zone is particularly advantageous for Iron Roughneck machines in reducing size and operability. An Iron Roughneck machine is a combined spinner and hydraulic wrench that both hydraulically power spins and torques the tool joints.
Machining the transition zone of drill pipe to make the transition zone smooth and cylindrical in the pipe mill or in the field by hand grinding is commercially impractical. Drill pipe is a standard interchangeable commodity. If a spinner maker were to specify that his machine can only be used with custom non-standard drill pipe with smooth transition zones it is unlikely that drilling contractors would buy it because the pipe would cost more than standard pipe, require field service, and not be interchangeable between rigs.